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Rethinking How We End A Satellite's Mission
At the end of their lives, most satellites fall to their death. Many of the smaller ones, including most of those going up as part of the “mega-constellations” currently under construction, are intended to burn up in the atmosphere. This Design for Demise (D4D) principle has unintended consequences, according to a paper by Antoinette Ott and Christophe Bonnal, both of whom work for MaiaSpace, a company designing reusable launch vehicles for the small satellite market.
NASA’s SPHEREx Observatory Completes Its First Map of the Cosmos in 102 Infrared Wavelengths
Launched in March, NASA’s SPHEREx space telescope has completed its first infrared map of the entire sky in 102 colors. This map will enable 3D distance measurements to other galaxies and allow astronomers to measure the influence of Cosmic Inflation on the large-scale structure of the Universe.
Why Active Rest Is Important During the Holidays
Sleep is often the first thing that many people associate with rest, but humans also require restorative downtime when awake
Turning Structural Failure into Propulsion
Solar sails have some major advantages over traditional propulsion methods - most notably they don’t use any propellant. But, how exactly do they turn? In traditional sailing, a ship’s captain can simply adjust the angle of the sail itself to catch the wind at a different angle. But they also have the added advantage of a rudder, which doesn’t work when sailing on light. This has been a long-standing challenge, but a new paper available in pre-print from arXiv, by Gulzhan Aldan and Igor Bargatin at the University of Pennsylvania describes a new technique to turn solar sails - kirigami.
Mathematicians spent 2025 exploring the edge of mathematics
Mathematicians spent 2025 exploring the edge of mathematics
Studying Physics in Microgravity
Studying Physics in Microgravity
In this Oct. 20, 2025, photo, tiny ball bearings surround a larger central bearing during the Fluid Particles experiment, conducted inside the Microgravity Science Glovebox (MSG) aboard the International Space Station’s Destiny laboratory module. A bulk container installed in the MSG, filled with viscous fluid and embedded particles, is subjected to oscillating frequencies to observe how the particles cluster and form larger structures in microgravity. Insights from this research may advance fire suppression, lunar dust mitigation, and plant growth in space. On Earth, the findings could inform our understanding of pollen dispersion, algae blooms, plastic pollution, and sea salt transport during storms.
In addition to uncovering potential benefits on Earth, research done aboard the space station helps inform long-duration missions like Artemis and future human expeditions to Mars.
Image credit: NASA/Zena Cardman
Studying Physics in Microgravity
In this Oct. 20, 2025, photo, tiny ball bearings surround a larger central bearing during the Fluid Particles experiment, conducted inside the Microgravity Science Glovebox (MSG) aboard the International Space Station’s Destiny laboratory module. A bulk container installed in the MSG, filled with viscous fluid and embedded particles, is subjected to oscillating frequencies to observe how the particles cluster and form larger structures in microgravity. Insights from this research may advance fire suppression, lunar dust mitigation, and plant growth in space. On Earth, the findings could inform our understanding of pollen dispersion, algae blooms, plastic pollution, and sea salt transport during storms.
In addition to uncovering potential benefits on Earth, research done aboard the space station helps inform long-duration missions like Artemis and future human expeditions to Mars.
Image credit: NASA/Zena Cardman
#775: The Hydrogen 21-cm Line
Atomic hydrogen is the raw material for stars, but there’s a problem. It’s cold & dark, but it can do a very rare trick, releasing a photon in a very specific wavelength, known as the 21 centimeter line. And thanks to this wavelength astronomers have mapped out star forming regions across the Milky Way, the Universe and into the Dark Ages! This forbidden transition of Hydrogen has led to the mapping of galaxy rotation, a cool classroom application of quantum mechanics, and weirdly no Nobel prize. In this episode, Fraser and Pamela take a look at this line’s out-of-proportion awesomeness!
Show Notes- The Power of the 21-Centimeter Line
- Why the 21-Centimeter Line Matters
- Seeing the Invisible Universe
- Galaxies, Dark Matter, and Hidden Mass
- Learning and Discovery
- Looking Back in Time
- Challenges and Future Solutions
- Beyond Astronomy
[Fraser Cain]
Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, I’m the publisher of Universe Today. With me, as always, is Dr. Pamela Gay, Senior Scientist for the Planetary Science Institute and the Director of CosmoQuest.
[Dr. Pamela Gay]
Hey, Pamela, how you doing? I am doing well enough. I am currently finding, I have new technology, which is absolutely amazing, but nothing works.
So everyone, thank you for your patience as there is ludicrous hacking that went into putting together this episode.
[Fraser Cain]
Now, normally, after the amount of time that I’ve been gone, I would say like, hey, it’s great to be back. And did you all miss me? But because you, in your infinite wisdom, said, let’s just record all these shows, get them in the can, and then you don’t have to think about this anymore.
We record all the shows, we got them in the can, and then I didn’t have to think about them anymore. And I am so glad you were so smart. You were so right, because I, because it is, you know, being on the road, it’s a gum show.
And trying to then set up internet of different time zones. It was so nice to go, oh, yeah, all those astronomy casts are done. So and now we continue uninterrupted, which was just great.
And so I’m back.
[Dr. Pamela Gay]
And you escaped, you escaped the CosmoQuest hangout-a-thon this year. There was no live recording of astronomy cast. You did not have to be part of our wild fundraising.
By the way, if anyone wants to donate money, please join both Fraser’s Patreon and my Patreon. We both need your support to keep doing what we do as independent journalists. All right, that’s done.
[Fraser Cain]
Yeah. Yeah. I mean, this will turn into a rant, so I don’t want.
But anyway, I’m finding that journalists are reaching out to me and saying, do you have any work?
[Dr. Pamela Gay]
Yeah, it’s really bad right now.
[Fraser Cain]
And that is telling me that the sort of copywriting apocalypse is starting to roll out. And fortunately, because we’re Patreon funded and we don’t use AI for our writing, we are going to be this island of stability as as the rest of this industry erodes all around us. So thank you, everybody, who supports us financially.
You are allowing me to pay everybody salaries. All right, let’s get into this week’s episode. Atomic hydrogen is the raw material for stars, but there’s a problem.
It’s cold and dark, but can do a very rare trick, releasing a photon in a very specific wavelength known as the 21 centimeter line. And thanks to this wavelength, astronomers have mapped out star forming regions across the Milky Way, the universe and into the dark ages. All right.
21 centimeter line. It’s a very obscure sounding topic. Yeah, very, very nerdy topic.
But it is like just one of the most useful tools that astronomers have at their disposal. And it’s kind of weird that we haven’t talked about this up until now. I mean, we’ve mentioned it, but I think, you know, let’s give it the the, you know, the appropriate amount of conversation.
[Dr. Pamela Gay]
And I have to admit, I had to go back and rewrite the show promo I initially wrote because I was quite certain that not only had we recorded an episode about this, which I determined we hadn’t, I was also quite certain that a Nobel Prize had been given to the 21 centimeter discovery humans, which it hadn’t. This is a line that’s like super, super important and just doesn’t seem to get the love it deserves.
[Fraser Cain]
Right. It will. It will.
[Dr. Pamela Gay]
It will.
[Fraser Cain]
Maybe after the show, we’re giving it the astronomy cast bump.
[Dr. Pamela Gay]
It’s true.
[Fraser Cain]
OK, so I guess let’s talk about. I’m trying to think. Let’s talk about molecular hydrogen, I guess, the raw material for stars.
[Dr. Pamela Gay]
So so molecular hydrogen. And just to be clear, the the 21 centimeter hydrogen line comes from atomic hydrogen. It comes from the atom of hydrogen.
[Fraser Cain]
Yeah.
[Dr. Pamela Gay]
So so molecular hydrogen take two hydrogen atoms. They each have one electron going around them in normal cases. And it turns out that that the electron shells and atoms really are completionists.
And I understand this is someone who is a completionist. You and hydrogen. Get all your tasks done.
Yes, exactly. And and so the S shell wants to have two electrons in it. So two hydrogens, they get close enough together like we can complete our shell if only we share our electrons.
And so they come together, they share their electrons, they complete their shell and they’re much happier this way. So this is the stuff of the cold, dark universe.
[Fraser Cain]
Right. Right. And and I think it’s really important to sort of understand, like when hydrogen receives a lot of radiation, then it starts to warm up.
It glows. Those are nebulae, right? We see them, but they don’t want to turn into stars.
They’re too hot.
[Dr. Pamela Gay]
Right. And so with 21 centimeter line, this is something that you don’t encounter in anything vaguely warm. So you’re now taking me in a direction I was not prepared for.
Where are we going?
[Fraser Cain]
Well, right. So I guess the point here is that that if you want to find clouds of hydrogen, clouds of hot hydrogen.
[Dr. Pamela Gay]
Yes.
[Fraser Cain]
All you have to do is look out there with a telescope.
[Dr. Pamela Gay]
Yeah. Hydrogen alpha. So so there’s there’s two major series of hydrogen lines that we look for, depending on what redshift we’re looking at.
So in the local universe, we have the bomber series, which is electrons jumping from higher energy levels down to the second energy level. Then at the ultraviolet locally, we have the Lyman series where Lyman alpha is two to one. And so it’s higher energy level into the first energy level.
And as things get redshifted further and further, that Lyman alpha eventually migrates into the visible wavelengths. And it allows us to see hydrogen at the highest redshifts out there up until the point when there’s no light going through the universe, when we have this foggy period before the universe reionized.
[Fraser Cain]
Right. And like I can look, I have nice dark skies here. I can look towards Orion and I can see the Orion Nebula.
[Dr. Pamela Gay]
Yes.
[Fraser Cain]
With my eyes.
[Dr. Pamela Gay]
Yes.
[Fraser Cain]
Right. There is this little glowy spot in Orion scabbard. And if you look in pair binoculars or telescope, then you definitely can see it.
And then you take a picture and you can absolutely see it. And so to see where the clouds of hydrogen are that are ionized, that are bright, glowing, you can it’s it’s not that challenging a problem. The what is the challenging problem is to find the hydrogen that is cold, the hydrogen that is that is has not been ionized is pumping out radiation that is cold.
And yet it is that cold hydrogen, which is the raw material for stars. And that’s where I’m going, is that astronomers need a technique to find the cold hydrogen.
[Dr. Pamela Gay]
Yeah. And and so what we’re looking for is the stuff that isn’t so dense that it’s blocking the light behind it. So it’s fairly easy to spot molecular clouds of super dense hydrogen.
They are great walls of blocking the rest of the galaxy.
[Fraser Cain]
Yeah.
[Dr. Pamela Gay]
So these are things like the Bach globules to see warm stuff. You have all these wonderful transitions and hydrogen that are quite happy to transition for you. So if you have hydrogen atoms that are not getting collisionally excited, that are not getting heated up by surrounding light, that are just cold, non-interacting, so diffuse, this this is like collisions are not a thing that an atom can expect to experience.
This is where you start to be able to imagine. And it turns out that it’s actually there that you can start to see what are called forbidden transitions. These are transitions that statistically we just should never have a chance of seeing.
[Fraser Cain]
Right.
[Dr. Pamela Gay]
And the specific forbidden line that we’re looking for is if you have a proton that has a spin up and you have an electron that has a spin up, that has a higher energy in that alignment than if you have them anti-aligned. So if the electron flips from spin up to spin down, or if you had the proton down, electron down and it flips to up, that flip between being aligned and being anti-aligned gives off a tiny amount of energy. And the smaller the amount of energy, the longer the wavelength of light.
[Fraser Cain]
Right.
[Dr. Pamela Gay]
And in this case, that length of light is is 21 centimeters is is your wavelength. So you’re going from something that is is like hair’s breadth to can measure it with your hands.
[Fraser Cain]
Yeah. Yeah. I mean, like when we talk about wavelengths of light, we’re talking, you know, often it’s like, oh, it’s 500 nanometers.
Are you thinking about visible light? And it is like we don’t have any practical experience to understand how small that is.
[Dr. Pamela Gay]
Yeah.
[Fraser Cain]
We talk about even infrared light. We’re looking at things that are in the micrometers to sub millimeter.
[Dr. Pamela Gay]
Yeah.
[Fraser Cain]
But but the you know, this thing, the 21 centimeter line, you know, it’s like about that.
[Dr. Pamela Gay]
Yeah.
[Fraser Cain]
And podcast listeners, I’m holding my hands out, you know, about two thirds of a foot. Right. Twenty twenty centimeters.
What what wavelength like what regime is that in? Is that in the microwave?
[Dr. Pamela Gay]
It’s it’s it’s part of the L band of microwave radio is where my brain puts it, because all of that is is something that you can measure with basically a radio dish. It’s just what is the horn you’re using? So this is part of a atmospheric hole that there’s there’s various wavelengths that are atmospheres like, no, you’re not allowed to observe that.
And this luckily falls into one of the bands that we can completely see from the surface of our world. And so when folks were starting to get a handle on quantum mechanics, we’re starting to get a handle on on these are all the different ways that energy can get released as protons and electrons flip and interact. It was predicted in nineteen forty four.
This this is a fairly new realization. It was predicted in nineteen forty four that this could be something that might be observable. And then in fifty one, they finally put together the set of observations to detect this super faint line.
And and the reason it’s faint is the the alignment that we’re looking for with with the aligned proton and electron that flipped to be anti aligned. That atomic situation is stable for eleven million years.
[Fraser Cain]
Right. So hold on. So so so I take a proton with its electron and I leave it.
And then if I wait eleven million years, that’s about how long it’s going to take for it to do that spin flip.
[Dr. Pamela Gay]
That that’s half life is the wrong word for this. But yeah, the probability of it flipping is probabilistically eleven million years.
[Fraser Cain]
Right. Probably it’ll probably happen.
[Dr. Pamela Gay]
Yeah.
[Fraser Cain]
In eleven million years. Right. And so if you have any one individual proton of hydrogen.
Yeah. It’s not going to do this in, you know, a thousand lifetimes, but you get a cloud that is large enough, then some number of them is is giving off this signal.
[Dr. Pamela Gay]
So you need to have a cloud that is excessively cold. So things aren’t moving around very much, excessively diffuse. So what little motion you’re going to have just because of the base temperature of our universe isn’t going to let these things collide with each other on timescales of tens of millions of years.
And then you need enough atoms that enough of these flips are occurring that we’re receiving enough light in our direction that it’s detectable.
[Fraser Cain]
OK, why? Why is this important? Why is this this this weird behavior of of atomic hydrogen?
Why does this matter?
[Dr. Pamela Gay]
I there’s a variety of different reasons. The first is it allows us to map out the least dense corners of our galaxy, the outer parts of the disk. It’s it’s like the line that we can catch from diffuse clouds of hydrogen.
I that are just barely gravitationally held on to. And it’s from these 21 centimeter measurements of our galaxy and other galaxies that folks like Vera Rubin were able to start saying, wait, these motions don’t what’s going on here.
[Fraser Cain]
And this is the person, not the telescope.
[Dr. Pamela Gay]
Right, right. The human being, the human being. Sorry.
That’s now a requirement to say, yes. Yeah. So so the human being who studied dark matter, right, along with other human beings who studied dark matter, were able to spot this flattening of the rotation curve of our galaxy, which isn’t something anyone expected.
It was expected that as the visible material dropped off, we we’d see the velocities decreasing with distance. Right. And they’re not, which says there’s a whole lot of stuff out there that that isn’t gassy enough to have forbidden lines.
[Fraser Cain]
Right. So that we look out in space and we see a galaxy and we see all of the stars, we see all the star forming regions, we see all the bright stuff.
[Dr. Pamela Gay]
Yeah.
[Fraser Cain]
But that is not the galaxy. There is more galaxy around that galaxy. There is also surrounded by clouds of hydrogen that will maybe eventually get pulled into stars or maybe get spun out or be sucked away through tidal tails, through interactions with other galaxies.
How big is that galaxy really? By mapping out this cold hydrogen, which is, I guess, more dense than just the than just intergalactic space.
[Dr. Pamela Gay]
Yes.
[Fraser Cain]
Right. There’s more stuff in that than there is just an intergalactic space. You can map out the real shape of the of the actual galaxy and all of the clouds of hydrogen that are surrounding it.
[Dr. Pamela Gay]
And this is something that we can do locally and a standard homework assignment at many universities that have small radio telescopes is to just assign a senior lab where you go out and you measure the 21 centimeter line in clouds of gas around the Milky Way and you do your own rotation curve repeating this historic work.
[Fraser Cain]
That’s amazing.
[Dr. Pamela Gay]
Yeah. It’s one of those things of it’s fundamental, but it’s repeatable in a way that you can’t deny that there’s unseen stuff that is out there when you see the data for yourself as a student.
[Fraser Cain]
But I think it’s important to like qualify that’s not dark matter like that’s that’s right. Dark comma matter. Right.
It is regular matter, regular hydrogen. You’re you know, you’re yeah, whatever. Seventy five percent made of the stuff.
[Dr. Pamela Gay]
Yeah.
[Fraser Cain]
Right. Or whatever. Right.
[Dr. Pamela Gay]
But dark matter is different stuff.
[Fraser Cain]
Different stuff. Yeah. React with the electromagnetic force.
So but and so like as an astronomer, you might be able to ask questions like how much gas is left in that galaxy that can form more stars? Where are the where are the reserves of gas in that galaxy? Do they line up with the spiral arms?
How do they transition between just clouds of gas to star forming regions? What is the potential of that galaxy? That’s where you’re you’re you’re mapping out using the 21 centimeter line.
[Dr. Pamela Gay]
And that that is the next place to go with this is so first you have, for me, the most interesting part, which is the discovering that not all the stuff that makes up a galaxy can be detected through through gravity allows us to see that that other stuff is out there. And then what is the potential for star formation? What is the potential for continued life?
What is the stuff available to feed supermassive black holes? There’s amazing maps of our own galaxy that allow you to see all throughout the disk of the Milky Way, the presence of 21 centimeter emission. And that’s telling us there is still gas and dust out there.
Not so dark that it blocks all the light, not so hot that it glows in bomber or Lyman lines of hydrogen transitions. It’s just out there being diffused and not colliding.
[Fraser Cain]
It’s it’s our war chest. It’s our it’s our gas reserves that the Milky Way can draw on for trillions of years into the future to make new stars. And the question, you know, the astronomers will ask this question, how many stars can this galaxy make?
It comes from the the cold. Sort of inert hydrogen that’s just sitting there, not glowing, not interacting, not blocking light, just being all right, so you take your microwave telescope, you tune it to 21 centimeters, you point it in the sky, thanks to the atmosphere, allowing that wavelength to get through. And then you just move around and you map out blobs here, blobs there and so on.
How does that then change as we want to look out into the cosmos, which, of course, is looking back in time?
[Dr. Pamela Gay]
So we have two ways to see the cold blobs of gas that haven’t bothered to get themselves into galaxies as we look out. So one of those is we see what are called the Lyman-alpha forest, where the light from background galaxies passes through clouds of gas that are between us and those galaxies. And at the redshift of those galaxies, we see the hydrogen lines of absorption.
Now, the other side of that is sometimes we are lucky enough to see the ever lengthening hydrogen 21 centimeter emission from those gas clouds. And once you start getting out to around 50 centimeters, you’re starting to look at cosmological distances where there really isn’t much light to give us a clue as to what’s going on. The only way we’re ever going to be able to detect light from the dark ages of our universe is to look for this extremely, extremely faint background light.
[Fraser Cain]
And you mentioned sort of 50 centimeters. So in other words, that the universe has been expanding, the wavelengths have been redshifting in the same way that what was once red light after the cosmic microwave background has turned into microwave. This light started out in the microwave and has now been redshifted to much longer wavelengths.
[Dr. Pamela Gay]
And there’s two different effects that does this. One is just as the universe expands, it expands the light with it. And the other is just the cosmological expansion of the universe adds its own redshift.
So it’s a really ugly calculation. But it means that while interesting things like Lyman Alpha, land in the visible, things that started out long ended up even longer.
[Fraser Cain]
Right. And so that takes a very special kind of telescope to see redshifted 21 centimeter long.
[Dr. Pamela Gay]
And and we haven’t gotten to the point yet that we’re starting to detect this this age before reionization from this light. It is something that we dream of doing, that we plan on doing.
[Fraser Cain]
Right.
[Dr. Pamela Gay]
But yeah, yeah, yeah.
[Fraser Cain]
And like I think it’s really important for people to understand, right? Like you, you had the beginning of the universe, you have the cosmic microwave background, the whole universe is kind of red and then it becomes transparent for the first time and then it cools down. But the first stars haven’t formed yet.
And so now we talked about those clouds of gas that are in the Milky Way. Imagine if the whole universe was that. Right.
Where is the stuff? Right. Well, you need the 21 centimeter line to show you where the stuff is.
So so that is the key to us understanding how those first galaxies, those first stars came together at a time when everything is obscured and you can’t see it. Wasn’t until all of those galaxies got going, the stars got going, they cleared out all the rest of that material and we could see them again. That’s the reionization you’re mentioning.
So so what are the sort of best ideas to do this? You mentioned we’re kind of at the cusp, like we really are at this point in the history of astronomy where this is a technique that is just within reach for us to be able to try and observe the first, you know, to map out this initial cold hydrogen. So, you know, what can we sort of count on, do you think?
[Dr. Pamela Gay]
Well, first of all, we need to get more detectors off our planet. That’s one of the big frustrations is as we get to this particular set of wavelengths, we’re fighting tooth and nail against the atmosphere, right? There there are atmospheric poles short word of this.
There are atmospheric poles long word of this. Right. This is a cursed wavelength.
[Fraser Cain]
Right. So you mentioned that if it was just a regular 21 centimeter line, then it gets to go through the atmosphere. But now it’s been redshifted.
So now the atmosphere is not playing nice with it anymore. Correct.
[Dr. Pamela Gay]
So building radio telescopes in space is something we have the capacity to do. But there’s other things that are a whole lot more interesting that like the James Webb Space Telescope is capable of looking at myriad different problems. A long wavelength radio telescope is going to be difficult to build.
You have to have really big dishes to get any kind of resolution or you have to have an interferometric system to get any sort of resolution because your resolution is dependent on the diameter divided by the wavelength. Your wavelength goes up. You need a bigger diameter to get the same wavelength to get the same resolution.
[Fraser Cain]
Right. But it’s also faint, right? Like it’s it’s faint, too.
So so an interferometer doesn’t get only gets you so far because you also need a telescope that can handle you need a lot of just antenna space. So you need something that is that has a large amount of resolving area and has a large baseline. Ideally, right.
So so have you like looked at some of the cool lunar telescopes to try and solve this problem?
[Dr. Pamela Gay]
They’re dead to me until they’re funded.
[Fraser Cain]
Right. Of course. Yes.
All right. Well, then I am going to explain this to you. Yes.
Which is that there are a bunch of teams that are working on ideas for moon based telescopes that would be on the far side of the moon. So we’ll be blocked by the by the the moon. And so you wouldn’t get the radiation coming from the earth.
All of our stupid, you know, radio traffic, you’d have this pristine, dark radio environment. And then they could build really big telescopes. And so the idea is where you would say land a spacecraft on the moon, you have a rover on board and it would reel out an antenna because you need to have you need to have like a big dish.
You can actually just have wire that you put down on the surface of the moon in a shape that that you need. And so you could have this sort of central lander and then rovers that are crawling out in all directions from it, laying down antenna onto the regolith that would form this gigantic antenna that’s blocked from the surface of the earth. There’s one called Far Side.
There’s one that NASA is working on. The Europeans are working on some ideas. The Chinese are actually going to be doing a test in a couple of years.
They’re going to send a radio telescope to the far side, but orbital of the moon and try to make some detections of the 21 centimeter line at the dark ages of the universe.
[Dr. Pamela Gay]
It’s super important to put this stuff on the far side of the moon because our atmosphere does leak these radio frequencies because we are literally using radio and television in this frequency band.
[Fraser Cain]
Yeah, we’re yelling in this frequency band and we would corrupt the results from radio telescope.
[Dr. Pamela Gay]
Right. So we have to block our own shouting. Yeah.
As as we look for this.
[Fraser Cain]
And there are enough plans now that one of these is going to happen. Like there are there was a prototype experiment that was on one of the lunar landers that toppled over.
[Dr. Pamela Gay]
Yeah.
[Fraser Cain]
And so they were going to try and make those observations. You’ve got like some tentative observations with things like the Murchison Array, which is the precursor to the Square Kilometer Array. You’re probably going to get some some detections using the Square Kilometer Array, but it’s sort of not its main job.
So it’s really going to be let’s put a telescope on the far side of the moon, a big, giant antenna or like a wire spooled out across the moon that will get us these observations. Because like the other ideas are like little Christmas trees, like what they’ve got with the Murchison Array. There’s been a lot of like really cool ideas.
Like it doesn’t have to look like a telescope, doesn’t even have to look like a big radio dish. It can be this very, very simple, very robust telescope. And yet it will do this job and detect.
And then there could be this time when astronomers are able to start to just get a sense of the density mapping out.
[Dr. Pamela Gay]
Yeah
[Fraser Cain]
You know how thick was this hydrogen early on when what was the separation between the clouds of hydrogen and the initial galaxies that were forming do we see the supermassive black holes forming first pulling in material from around them so there’s a lot of yeah yeah I mean it’s it’s called the dark ages for a reason
[Dr. Pamela Gay]
Right and and there’s one other obscure usage of this line that we haven’t talked about and and that’s the idea that lots of different space observing civilizations would probably want to protect just as we’ve protect protected this line from being used for everyday transmission so we don’t have radio stations or television stations using this wavelength because it’s reserved for astronomy now you can start to imagine that if that is a common habit preserving wave bands for science that there could be civilizations out there that decide they’re going to transmit purposefully making their existence known at this particular wavelength so it’s been proposed that the 21 centimeter line also works for SETI potentially
[Fraser Cain]
I love that
[Dr. Pamela Gay]
yeah so I I particularly love the idea that wanting to do science is something we should expect to be a universal idea of civilizations and I really hope it’s true I really hope that’s all wonderful
[Fraser Cain]
thanks Pamela
[Dr. Pamela Gay]
thank you Fraser and thank you to everyone out there in our patreon audience you are all amazing this show is made possible by our community on patreon.com slash astronomy cast this week we’d like to thank the following $10 and up patrons Adam Anise Brown Alexis Andy Moore Astrobop Bebop Apocalypse Bob Zatzke Brett Moorman Burry Gowman Cody Rose Daniel Loosley David Gates Dizastrina Dwight Ilk Evil Melky Flower Guy Galactic President Scooper Star McScoopsalot Glenn McDavid Greg Vylde Helge Bjorkhog Jarvis Earl Jeff Wilson Jim of Everett John Drake Jonathan H Staver Justin S Kenneth Ryan Kinsella Panflenko Lee Harbourn Marco Iorassi Mark Steven Raznak Matthias Hayden Michael Wichman Mike Hizzi Nick Boyd Paul D Disney Pauline Middleink Randall Robert Cordova Sergio Sanchevier Sergio San Severo Shersom Semyon Torfason Slug Taz Tully The Lonely Sandperson Time Lord Iroh Van Ruckman Will Hamilton thank you all so very much
[Fraser Cain]
great all right thanks everyone and we will see you next week
[Dr. Pamela Gay]
bye-bye everyone
Live ShowBefore We Build on the Moon, We Have to Master the Commute
Even most rocket scientists would rather avoid hard math when they don’t have to do it. So when it comes to figuring out orbits in complex three-body systems, like those in Cis-lunar space, which is between the Earth and the Moon, they’d rather someone else do the work for them. Luckily, some scientists at Lawrence Livermore National Laboratory seems to have a masochistic streak - or enough of an altruistic one that it overwhelmed the unpleasantness of doing the hard math - to come up with an open-source dataset and software package that maps out 1,000,000 cis-lunar orbits.